4.3BSD-UWisc/man/man5/passwd.5

.\" @(#)passwd.5 1.1 85/12/28 SMI; from UCB 4.2
.TH PASSWD 5 "1 February 1985"
.SH NAME
passwd \- password file
.SH SYNOPSIS
.B /etc/passwd
.SH DESCRIPTION
.IX  "passwd file"  ""  "\fLpasswd\fP \(em password file"
.LP
The
.I passwd
file contains for each user the following information:
.IP name 10
User's login name \(em contains no upper case characters and must not be
greater than eight characters long.
.IP password 10
encrypted password
.IP "numerical user ID" 10
This is the user's ID in the system and it must be unique.
.IP "numerical group ID" 10
This is the number of the group that the user belongs to.
.IP "user's real name" 10
In some versions of UNIX, this field also contains the user's office,
extension, home phone, and so on.  For historical reasons this field is
called the
.SM GCOS
field.
.IP "initial working directory" 10
The directory that the user is positioned in when they log in \(em this
is known as the `home' directory.
.IP shell 10
program to use as Shell when the user logs in.
.LP
The user's real name field may contain `&', meaning insert the login name.
.LP
The password file is an
.SM ASCII
file.  Each field within each user's entry
is separated from the next by a colon.  Each user is separated from the
next by a new-line.  If the password field is null, no password is demanded;
if the Shell field is null,
.I /bin/sh
is used.
.LP
The
.I passwd
file can also have line beginning with a plus (+),
which means to incorporate entries from the yellow pages.
There are three styles of + entries:
all by itself, + means to insert the entire contents
of the yellow pages password file at that point;
.I +name
means to insert the entry (if any) for
.I name
from the yellow pages at that point;
.I +@name
means to insert the entries for all members of the network group
.I name
at that point.
If a + entry has a non-null password, directory, gecos, or shell field,
they will overide what is contained in the yellow pages.
The numerical user ID and group ID fields cannot be overridden.
.SH EXAMPLE
.LP
Here is a sample
.I /etc/passwd
file:
.IP
.ft L
.nf
root:q.mJzTnu8icF.:0:10:God:/:/bin/csh
tut:6k/7KCFRPNVXg:508:10:Bill Tuthill:/usr2/tut:/bin/csh
+john:
+@documentation:no-login:
+:::Guest
.fi
.LP
In this example, there are specific entries for users
.I root
.and
.IR tut ,
in case the yellow pages are out of order.
The user
.L john
will have his password entry in the yellow pages
incorporated without change;
anyone in the netgroup
.I documentation
will have their password field disabled,
and anyone else will be able to log in with their usual password,
shell, and home directory, but with a gecos field of
.I Guest.
.LP
The password file resides in the
.I /etc 
directory.  Because of the encrypted passwords,
it has general read permission and can be used,
for example, to map numerical user ID's to names.
.LP
Appropriate precautions must be taken to lock the 
.I /etc/passwd
file against simultaneous changes if it is to be edited with a text editor;
.IR vipw (8)
does the necessary locking.
.SH FILES
/etc/passwd
.SH "SEE ALSO"
getpwent(3), login(1), crypt(3), passwd(1), group(5), vipw(8), adduser(8)